Caring for cats with hyperthyroidism

Radioactive Iodine (l-131) Treatment for Cats

SHCH is Located on Sydney’s North Shore

Vet Referrals welcome.
Cat Owners can book directly.

Feline Hyerthyroidism and its symptoms

Feline hyperthyroidism occurs when the thyroid gland becomes enlarged and produces excess thyroid hormone. It is a very common disease in older cats.


Possible symptoms might include

  • ^Increased vocalisation
  • ^Fast heart and breathing rates
  • ^ Increased appetite and weight loss
  • ^Vomiting and diarrhoea
  • ^ Increase in thirst

Left untreated it becomes a life threatening illness. Untreated cats can develop heart disease and problems with blood pressure, kidneys, and other organs.

Treatment options for Hyperthyroidism in cats

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Radioactive Iodine Treatment

Radioactive iodine treatment is recognised worldwide as being the gold standard treatment for feline hyperthyroidism. Studies show that cats treated with radioactive iodine live longer than those treated with daily medical management.

A single treatment will cure 95% of cats. It is a safe treatment with minimal side effects.

The radioactive iodine is administered by a capsule and is only taken up in the thyroid gland, destroying the overactive tissue whilst having no adverse effects on the rest of the body. Due to EPA guidelines your cat must stay with us in hospital for one week until the radiation levels are sufficiently low to be discharged.

Daily Medication

These prescription drugs block the production of thyroid hormone. They are often quite effective in controlling symptoms but treatment is lifelong.

The treatments can be expensive over time as they involve regular blood tests to monitor dose and its effect on the body. Often increased doses are required as time goes on and depending on the specific drug, efficacy can be variable.

We mainly recommend this when concurrent disease may prohibit more curative treatments. Vomiting, diarrhoea, and loss of appetite can occur as side effects of these medications, but they are usually mild and self-limiting.

Occasionally more serious side effects can occur such as liver toxicity, skin conditions, and low white blood cell counts.


Surgery to remove the thyroid gland is a complex specialist surgical procedure. It has risks associated with anaesthesia in an older cat and possible parathyroid gland damage that can result in calcium imbalances.

This is rarely performed as the risks outweigh the benefits when radioactive iodine is available as it is also a long term cure.


A specific iodine restricted diet is commercially available that reduces thyroid hormone production.

The diet must be strictly adhered to (with no other foods given at all) and its long-term safety is not

Benefits of radioactive iodine treatment

  • ZNo daily medication
  • Z No regular blood tests
  • ZIt is a safe cure without anaesthesia
  • ZNon-invasive: Unlike surgery.
  • ZMore cost-effective in the long run

What does the treatment cost

When you add up the costs of medications, blood tests and regular vet visits, the cost of treating a cat over a one-year period with daily medication is similar to the cost of radioactive iodine treatment ($1850). Most cats with uncomplicated hyperthyroidism will live several years following radioactive iodine treatment, unless they develop another disease.

Thus it ends up paying off to treat the hyperthyroidism once at the beginning with radioactive iodine-131 and also saves you the hassle of medicating your cat daily. There is more detail on costs in our FAQs section.

Some kind words

To Dr Martine, Karina, Michaele, Gina, Dani, Sabine, Tess, Dani, Kylie and all the other wonderful staff at SHCH.

Thank you so much! For taking such good care of precious Xena, your daily messages of reassurance were very comforting.

My experience with SHCH has been a positive one 😊.
You are all angels.

From A, D & Xena

One of my babies, nearly 15-year-old Indianna, was diagnosed in a routine check-up with having an over active thyroid. Dr Martine explained that this condition over time would cause other health problems even with the daily medication keeping it at bay and suggested we treat him with radioactive iodine treatment…

…When his radiation levels were safe, I bought him home. I was so happy to have him back, even his naughty nearly 11-year-old little sister had missed him.

He settled back home quickly and after his blood test a few weeks later Martine found his levels in his thyroid were normal. So he is cured !

I have never regretted him having this treatment. I can’t thank Martine and the team enough for looking after him, I received daily updates on how he was and I appreciate all the help, kindness and understanding they showed Indianna and myself. I knew he was in the best hands.

C Vella